prevent colorToAlpha from carrying over from one imagery layer to its replacement
prevent colorToAlpha from carrying over from one imagery layer to its replacement

geoscan/cesium,likangning93/cesium,CesiumGS/cesium,josh-bernstein/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,geoscan/cesium,progsung/cesium,josh-bernstein/cesium,jasonbeverage/cesium,likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,YonatanKra/cesium,AnalyticalGraphicsInc/cesium,kaktus40/cesium,CesiumGS/cesium,kaktus40/cesium,jasonbeverage/cesium,progsung/cesium,YonatanKra/cesium,YonatanKra/cesium,CesiumGS/cesium,YonatanKra/cesium,likangning93/cesium,likangning93/cesium